Re: [PATCH] selftests/clone3: Fix capability dropping by using standard libcap API

["Lai, Yi" <yi1.lai@intel.com>]

On Wed, Apr 01, 2026 at 09:11:59AM +0800, Lai, Yi wrote:
> On Tue, Mar 31, 2026 at 02:10:09PM -0600, Shuah Khan wrote:
> > On 3/9/26 21:14, Yi Lai wrote:
> > > The clone3_cap_checkpoint_restore.c selftest defined its own 'struct
> > > libcap' to manually cast and manipulate the internal memory layout of
> > > the opaque 'cap_t' type.
> > > 
> > > Starting with libcap v2.60 (commit aca076443591 "Make cap_t operations
> > > thread safe"), a '__u8 mutex' was added to the beginning of the internal
> > > 'struct _cap_struct'. This structural shift breaks the selftest's custom
> > > struct layout assumptions, causing capability corruption and leading to
> > > failures during test execution.
> > > 
> > > Fix this by removing the custom struct definition and use the standard
> > > cap_set_flag() API.
> > 
> > What king of failures are you seeing? Can you send the failures from
> > the run?
> > 
> 
> I can reproduce the failure on CentOS Stream 10 with libcap 2.69:
> 
> TAP version 13
> 1..1
> # Starting 1 tests from 1 test cases.
> #  RUN           global.clone3_cap_checkpoint_restore ...
> # clone3() syscall supported
> # clone3_cap_checkpoint_restore.c:151:clone3_cap_checkpoint_restore:Child has PID 10647
> cap_set_proc: Operation not permitted
> # clone3_cap_checkpoint_restore.c:160:clone3_cap_checkpoint_restore:Expected set_capability() (-1) == 0 (0)
> # clone3_cap_checkpoint_restore.c:161:clone3_cap_checkpoint_restore:Could not set CAP_CHECKPOINT_RESTORE
> # clone3_cap_checkpoint_restore: Test terminated by assertion
> #          FAIL  global.clone3_cap_checkpoint_restore
> not ok 1 global.clone3_cap_checkpoint_restore
> # FAILED: 0 / 1 tests passed.
> # Totals: pass:0 fail:1 xfail:0 xpass:0 skip:0 error:0
> 
> After applying the proposed fix patch that uses standard libcap APIs,
> the test passes in my test environment. It also passes on CentOS Stream
> 9 with libcap 2.48 (<2.60).
>

Hi Shuah,

Do you have concerns in terms of this fix? Please let me know if any
suggestions.

Thank you,
Yi Lai
 
> Regards,
> Yi Lai
> 
> > > 
> > > Fixes: 1d27a0be16d6 ("selftests: add clone3() CAP_CHECKPOINT_RESTORE test")
> > > Signed-off-by: Yi Lai <yi1.lai@intel.com>
> > > ---
> > 
> > thanks,
> > -- Shuah